A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives a fuel such as hydrogen gas and the cathode receives a fluid such as oxygen or air. Several fuel cells are typically combined in a fuel cell stack to generate a desired amount of power. A typical fuel cell stack for a vehicle may include several hundred individual cells. Typically, the fluid is caused to flow through the stack by a compressor. Oxygen not consumed in the stack is expelled as a cathode exhaust gas that may include water as a stack by-product.
Pressure regulators are employed in fuel cell systems at various locations to control pressures and flow rates. For example, pressure regulators may be employed at the anode side of the fuel cell stack to provide a pressure reduction of the hydrogen gas flowing from a hydrogen pressure storage tank and at an anode inlet to the stack. At the output of the hydrogen pressure tank, the pressure regulator may be required to reduce the pressure from 30-700 bar (abs) to 4-9 bar (abs). At the input to the anode side of the fuel cell stack, the pressure reduction may be from 4-9 bar (abs) to 1-2 bar (abs). In both of these applications, the hydrogen flow rate may vary between 0.02 and 2.0 g/s. These parameters provide a regulator turn-down ratio or range of operation of about 1:100.
Known pressure regulators are generally designed for turn-down ratios in the range of 1:10 to 1:20, and typically require a relatively constant inlet pressure. Such pressure regulators are typically not suitable for fuel cell system applications because of the accurate pressure regulation required at low flow rates and tight flow control necessary for the anode input.
It would be desirable to develop a pressure regulator capable of accommodating high turn down ratios, wherein an accuracy in accommodating low flow rates is maximized.